Situations arise when it is desirable to know that a document existed on or before a certain date. For example, in the field of research and development, it may be desirable to know when a document existed to firmly establish who was first in the race to be the inventor, and approximately when the invention had been made. This may be particularly true for scanned paper documents.
One of the most common means for determining when an electronic document has been created is to look at the date/time stamp of the document as set by the operating system. In the large majority of cases, where trust is not an issue, this date/time stamp is sufficient to date the document. However, the date/time stamp provided by the operating system can be easily modified, and so may be deemed unsatisfactory by an untrusting but interested party.
One method used to verify and establish the dating of an electronic document is to give the other party full access to the server that contains the document, and to research the evolution of ideas and other documents that led up to the document in question. For example, in the field of software, with great patience and an enormous amount of time, it is possible for another party to determine the evolution of a piece of software as it goes through numerous coding and debugging cycles (the results of which are typically not deleted from the server), and thus establish with a fair amount of confidence that the version of the software in question did indeed exist on a certain date. However, giving another party access to a server is a risky undertaking, which many companies and individuals are uneasy to do. To ensure that other trade secrets on the server are not compromised during the search, careful surveillance is required. As the process can be quite time-consuming, this surveillance can quickly become expensive and burdensome.
As an alternative, trusted escrow services exist that will archive copies of documents, and vouch for the dates and times at which the documents were submitted. This is a considerable improvement over granting a potentially hostile party access to a server, and determining the submission date and time of the document is basically automatic, being provided by the escrow service. However, a company or person can never know in advance which documents will be critical, for which the creation date of the document will become an issue, and which documents will not. Of course, the vast majority of documents will never be of critical importance. However, to make certain that when the day comes a document can be produced and dated on demand, all potential documents must be submitted to the escrow service. As escrow services typically charge by the number of documents submitted, and by the number of updates, costs can quickly grow.
It would therefore be desirable to have a method that would quickly, easily and cheaply enable a third party to establish with credible certainty that a host of electronic documents existed on a certain date and time.